Stop rebuilding the task manager list view after every new row added.
Stop rebuilding the task manager list view after every new row added.

BUG=69391
TEST=Create lots of new tabs, bring up task manager, should be fast.

Review URL: http://codereview.chromium.org/6240001

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@71815 0039d316-1c4b-4281-b951-d872f2087c98

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